The crew of a twin-propellor TransAsia plane which crashed into a river in Taipei killing 35 people had lost power in one engine but shut down and restarted the other, investigators said on Friday.
The reason for the pilots' action was unclear but a combined lack of thrust caused the almost-new turboprop ATR 72-600 to stall soon after take-off, Aviation Safety Council officials said after a preliminary study of 'black box' flight recorders.
The plane, which can fly on one engine, was carrying 58 passengers and crew when it lurched nose-up between buildings, clipped an overpass and a taxi with one of its wings and then crashed upside down into a shallow river on Wednesday. Fifteen people survived.
The cockpit data and voice recorders showed that the plane warned five times of stalling before the crash in the center of Taipei, according to findings by the council.
The right engine entered a state called "auto-feather", in which it reduced thrust to the propeller, Thomas Wang, managing director of the council, told a news briefing.
The flight crew then reduced power to the left engine, turned it off and attempted to restart it, but it did not gain enough thrust.
There was no word on what may have been going through the pilots' minds or what the instruments may have been telling them, but evidence presented so far will raise questions over whether they accidentally cut the wrong engine.
"That happens, but it is rare," said Paul Hayes, safety director at British aviation consultancy Ascend Flightglobal.
In 1989, a British Midlands Boeing 737 jet crashed in central England after the crew shut down the wrong engine. Investigators said unfamiliar vibration and noise contributed to the so-called Kegworth disaster, in which 47 passengers died.
Taiwan said the TransAsia problems began shortly after the turboprop aircraft left Taipei's downtown Songshan airport.
"The first engine experienced a problem 37 seconds after take-off at 1,200 feet," Wang said.
He said the pilot had announced a "flameout", which can occur when fuel supply to an engine is interrupted or when there is faulty combustion, but that there had not been one according to the data.
"The flight crew stepped on the accelerator of engine 2 (righthand side)... The engine was still operating, but neither engine produced power."
Pilots' effort to save plane
The plane was powered by two PW127M engines made by Pratt & Whitney, part of United Technologies.
A fuller report on the crash will be available in next 30 days, with a final one expected in the next three to six months. For now, investigators cannot say exactly what caused the crash.
The pilot, 42-year-old Liao Chien-tsung, has been praised by Taipei's mayor for steering the plane between apartment blocks and commercial buildings before ditching the stalled aircraft in a river.
The bodies of Liao and his co-pilot were retrieved from the cockpit, with their legs badly broken, investigators said.
"They were still trying to save this aircraft until the last minute," media quoted unidentified prosecutors involved in the crash investigation as saying.
Eight people are still missing. Aviation officials have said they have not given up hope of finding them.
The plane was bound for the Taiwan island of Kinmen. Among those on board were 31 tourists from China, mainly from the southwestern city of Xiamen.
Taiwan's aviation regulator has ordered TransAsia and Uni Air, a subsidiary of EVA Airways Corp, to conduct engine and fuel system checks on the remaining 22 ATR aircraft they still operate.
The crash was the latest in a string of Asian air disasters.
Indonesia has expanded its search for bodies of Indonesia AirAsia Flight QZ8501 that crashed into the Java Sea in December, killing all 162 people on board.
After a lull in search and recovery efforts, more bodies and wreckage have been found in the past few days off the coast of the Indonesian island of Sulawesi. A total of 96 bodies have been found.